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Download NCERT Solutions for Class 9 - Maths, Science, Hindi, ramblipetasga.gq in PDF. This PDF is based NCERT books and their answers are also given to study online. Revision boos Solutions of Maths for class 9th is given below to download. Easy to carry class 9th NCERT / CBSE Textbooks in your pocket – Download This Free App from your Android Phone or Tablet. Application provides Fastest. Download Study Material for preparation of 9th for free. NCERT 9th CLASS BOOKS IN PDF: Hindi was published in The file is available in PDF format.
Many substances exhibit multiple solid phases. For example, there are three phases of solid iron alpha, gamma, and delta that vary based on temperature and pressure.
A principal difference between solid phases is the crystal structure , or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the aqueous phase, which is the state of substances dissolved in aqueous solution that is, in water.
Less familiar phases include plasmas , Bose—Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in biology.
Bonding Main article: Chemical bond An animation of the process of ionic bonding between sodium Na and chlorine Cl to form sodium chloride , or common table salt. Ionic bonding involves one atom taking valence electrons from another as opposed to sharing, which occurs in covalent bonding Atoms sticking together in molecules or crystals are said to be bonded with one another. A chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them.
A chemical bond can be a covalent bond , an ionic bond , a hydrogen bond or just because of Van der Waals force. Each of these kinds of bonds is ascribed to some potential.
These potentials create the interactions which hold atoms together in molecules or crystals. In many simple compounds, valence bond theory , the Valence Shell Electron Pair Repulsion model VSEPR , and the concept of oxidation number can be used to explain molecular structure and composition.
An ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non-metal atom, becoming a negatively charged anion. The two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them.
The ions are held together due to electrostatic attraction, and that compound sodium chloride NaCl , or common table salt, is formed. In the methane molecule CH4 , the carbon atom shares a pair of valence electrons with each of the four hydrogen atoms.
Thus, the octet rule is satisfied for C-atom it has eight electrons in its valence shell and the duet rule is satisfied for the H-atoms they have two electrons in their valence shells. In a covalent bond, one or more pairs of valence electrons are shared by two atoms: the resulting electrically neutral group of bonded atoms is termed a molecule.
Atoms will share valence electrons in such a way as to create a noble gas electron configuration eight electrons in their outermost shell for each atom. Atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule.
However, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium , which has two electrons in its outer shell. Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes , valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used.
See diagram on electronic orbitals. Energy Main article: Energy In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic , molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved.
Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants.
A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. A reaction is said to be exothermic if the reaction releases heat to the surroundings; in the case of endothermic reactions , the reaction absorbs heat from the surroundings. Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy.
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